1. Technical Field
The present invention relates generally to heterogeneously catalyzed reactions. More particularly, the present invention relates to an apparatus and process for contacting reactants with a catalyst whereby a desired product is obtained.
2. Background of the Invention
The rate of chemical reactions involving liquids, gases and solids depend on time of contact, temperature, and pressure. In cases where it is desirable to react two or more raw materials of different phases (e.g. solid and liquid; liquid and gas; solid, liquid and gas), one of the limiting factors controlling the rate of reaction involves the contact time of the reactants. When reaction rates are accelerated, residence times may be decreased, thereby increasing obtainable throughput.
In the case of heterogeneously catalyzed reactions there is the additional rate limiting factor of having the reacted products removed from the surface of the solid catalyst to permit the catalyst to catalyze further reactants. Contact time for the reactants and/or catalyst is often controlled by mixing which provides contact with reactants involved in a chemical reaction.
Not to be limited by theory, it is known in emulsion chemistry that sub-micron particles, or bubbles, dispersed in a liquid undergo movement primarily through Brownian motion effects. Such sub-micron sized particles or bubbles may have greater mobility through boundary layers of solid catalyst particles, thereby facilitating and accelerating the catalytic reaction through enhanced transport of reactants.
The use of small sized solid catalyst particles in slurry reactors and fixed bed reactors presents problems. For example, in instances where the reaction to be catalyzed is highly exothermic (e.g., Fischer-Tropsch conversion of gases to liquid hydrocarbons), fixed bed operation may be unsuitable due to the inability to adequately control the reactor temperature. Slurry operation may overcome the temperature control issue, but concomitantly presents the issue of separating the small catalyst particles from the product prior to recycle, disposal and/or regeneration of the catalyst and sale or further processing of the product.
Accordingly, there is a need in industry for improved apparatus, systems and processes for contacting reactants with solid catalyst.